fix: Handle stalled async task in MapCache (#11015)

apps/explorer/lib/explorer/chain/cache/address_sum.ex

@@ -17,9 +17,10 @@ defmodule Explorer.Chain.Cache.AddressSum do
   alias Explorer.Etherscan
 
   defp handle_fallback(:sum) do
-    # This will get the task PID if one exists and launch a new task if not
+    # This will get the task PID if one exists, check if it's running and launch
+    # a new task if task doesn't exist or it's not running.
     # See next `handle_fallback` definition
-    get_async_task()
+    safe_get_async_task()
 
     {:return, Decimal.new(0)}
   end
@@ -49,7 +50,7 @@ defmodule Explorer.Chain.Cache.AddressSum do
 
   # By setting this as a `callback` an async task will be started each time the
   # `sum` expires (unless there is one already running)
-  defp async_task_on_deletion({:delete, _, :sum}), do: get_async_task()
+  defp async_task_on_deletion({:delete, _, :sum}), do: safe_get_async_task()
 
   defp async_task_on_deletion(_data), do: nil
 end

apps/explorer/lib/explorer/chain/cache/address_sum_minus_burnt.ex

@@ -17,9 +17,10 @@ defmodule Explorer.Chain.Cache.AddressSumMinusBurnt do
   alias Explorer.Chain.Cache.Helper
 
   defp handle_fallback(:sum_minus_burnt) do
-    # This will get the task PID if one exists and launch a new task if not
+    # This will get the task PID if one exists, check if it's running and launch
+    # a new task if task doesn't exist or it's not running.
     # See next `handle_fallback` definition
-    get_async_task()
+    safe_get_async_task()
 
     {:return, Decimal.new(0)}
   end
@@ -56,7 +57,7 @@ defmodule Explorer.Chain.Cache.AddressSumMinusBurnt do
 
   # By setting this as a `callback` an async task will be started each time the
   # `sum_minus_burnt` expires (unless there is one already running)
-  defp async_task_on_deletion({:delete, _, :sum_minus_burnt}), do: get_async_task()
+  defp async_task_on_deletion({:delete, _, :sum_minus_burnt}), do: safe_get_async_task()
 
   defp async_task_on_deletion(_data), do: nil
 end

apps/explorer/lib/explorer/chain/cache/block.ex

@@ -56,9 +56,10 @@ defmodule Explorer.Chain.Cache.Block do
   end
 
   defp handle_fallback(:count) do
-    # This will get the task PID if one exists and launch a new task if not
+    # This will get the task PID if one exists, check if it's running and launch
+    # a new task if task doesn't exist or it's not running.
     # See next `handle_fallback` definition
-    get_async_task()
+    safe_get_async_task()
 
     {:return, nil}
   end
@@ -95,7 +96,7 @@ defmodule Explorer.Chain.Cache.Block do
 
   # By setting this as a `callback` an async task will be started each time the
   # `count` expires (unless there is one already running)
-  defp async_task_on_deletion({:delete, _, :count}), do: get_async_task()
+  defp async_task_on_deletion({:delete, _, :count}), do: safe_get_async_task()
 
   defp async_task_on_deletion(_data), do: nil
 

apps/explorer/lib/explorer/chain/cache/gas_price_oracle.ex

@@ -310,9 +310,10 @@ defmodule Explorer.Chain.Cache.GasPriceOracle do
   defp fast_time_coefficient, do: Application.get_env(:explorer, __MODULE__)[:fast_time_coefficient]
 
   defp handle_fallback(:gas_prices) do
-    # This will get the task PID if one exists and launch a new task if not
+    # This will get the task PID if one exists, check if it's running and launch
+    # a new task if task doesn't exist or it's not running.
     # See next `handle_fallback` definition
-    get_async_task()
+    safe_get_async_task()
 
     {:return, get_old_gas_prices()}
   end
@@ -353,7 +354,7 @@ defmodule Explorer.Chain.Cache.GasPriceOracle do
   # `gas_prices` expires (unless there is one already running)
   defp async_task_on_deletion({:delete, _, :gas_prices}) do
     set_old_gas_prices(get_gas_prices())
-    get_async_task()
+    safe_get_async_task()
   end
 
   defp async_task_on_deletion(_data), do: nil

apps/explorer/lib/explorer/chain/cache/gas_usage.ex

@@ -37,9 +37,10 @@ defmodule Explorer.Chain.Cache.GasUsage do
   end
 
   defp handle_fallback(:sum) do
-    # This will get the task PID if one exists and launch a new task if not
+    # This will get the task PID if one exists, check if it's running and launch
+    # a new task if task doesn't exist or it's not running.
     # See next `handle_fallback` definition
-    get_async_task()
+    safe_get_async_task()
 
     {:return, nil}
   end
@@ -73,7 +74,7 @@ defmodule Explorer.Chain.Cache.GasUsage do
 
   # By setting this as a `callback` an async task will be started each time the
   # `sum` expires (unless there is one already running)
-  defp async_task_on_deletion({:delete, _, :sum}), do: get_async_task()
+  defp async_task_on_deletion({:delete, _, :sum}), do: safe_get_async_task()
 
   defp async_task_on_deletion(_data), do: nil
 

apps/explorer/lib/explorer/chain/cache/pending_block_operation.ex

@@ -35,9 +35,10 @@ defmodule Explorer.Chain.Cache.PendingBlockOperation do
   end
 
   defp handle_fallback(:count) do
-    # This will get the task PID if one exists and launch a new task if not
+    # This will get the task PID if one exists, check if it's running and launch
+    # a new task if task doesn't exist or it's not running.
     # See next `handle_fallback` definition
-    get_async_task()
+    safe_get_async_task()
 
     {:return, nil}
   end
@@ -67,7 +68,7 @@ defmodule Explorer.Chain.Cache.PendingBlockOperation do
 
   # By setting this as a `callback` an async task will be started each time the
   # `count` expires (unless there is one already running)
-  defp async_task_on_deletion({:delete, _, :count}), do: get_async_task()
+  defp async_task_on_deletion({:delete, _, :count}), do: safe_get_async_task()
 
   defp async_task_on_deletion(_data), do: nil
 end

apps/explorer/lib/explorer/chain/cache/transaction.ex

@@ -36,9 +36,10 @@ defmodule Explorer.Chain.Cache.Transaction do
   end
 
   defp handle_fallback(:count) do
-    # This will get the task PID if one exists and launch a new task if not
+    # This will get the task PID if one exists, check if it's running and launch
+    # a new task if task doesn't exist or it's not running.
     # See next `handle_fallback` definition
-    get_async_task()
+    safe_get_async_task()
 
     {:return, nil}
   end
@@ -68,7 +69,7 @@ defmodule Explorer.Chain.Cache.Transaction do
 
   # By setting this as a `callback` an async task will be started each time the
   # `count` expires (unless there is one already running)
-  defp async_task_on_deletion({:delete, _, :count}), do: get_async_task()
+  defp async_task_on_deletion({:delete, _, :count}), do: safe_get_async_task()
 
   defp async_task_on_deletion(_data), do: nil
 end

apps/explorer/lib/explorer/chain/map_cache.ex

@@ -201,6 +201,35 @@ defmodule Explorer.Chain.MapCache do
     end
   end
 
+  defp named_functions(:async_task) do
+    quote do
+      def get_async_task, do: get(:async_task)
+
+      @doc """
+      Checks if the asynchronous task has stalled (has finished, but still in cache),
+      and if so, creates a new replacement task to continue the operation.
+      """
+      def safe_get_async_task do
+        case get_async_task() do
+          pid when is_pid(pid) ->
+            if Process.alive?(pid) do
+              pid
+            else
+              set_async_task(nil)
+              get_async_task()
+            end
+
+          not_pid ->
+            not_pid
+        end
+      end
+
+      def set_async_task(value), do: set(:async_task, value)
+
+      def update_async_task(value), do: update(:async_task, value)
+    end
+  end
+
   # sobelow_skip ["DOS"]
   defp named_functions(key) do
     quote do